1. Field of the Invention
The present invention relates to a process of purging a semiconductor manufacturing apparatus, more specifically, to a purge step for a CVD (chemical vapor deposition) apparatus after dry-cleaning step.
2. Description of the Related Art
When a semiconductor manufacturing apparatus, for example, a CVD apparatus such as a LP (low pressure)-CVD apparatus is used, silicon, silicon oxides, silicon nitrides, and/or thin-film materials to be used in a semiconductor device are deposited within a reaction chamber (which Hereinafter will be referred as a “chamber”) of the manufacturing apparatus. When such a CVD-deposited film is formed excessively thick, a problem occurs that peel of the film occurs, and inside of the chamber is thereby contaminated. In addition, when the film peel has occurred to make the thickness of deposited films in the chamber non-uniform, CVD films formed over semiconductor wafers are not formed to be uniform. Then, conventionally, before such problem become remarkable, an etching process is performed to remove the deposited films by using a cleaning gas containing halogen such as ClF3 or F2. Generally, when the film thickness over a monitor wafer placed in the chamber has exceeded a predetermined level, the inside of the chamber is dry-cleaned for a time determined to be sufficient by experience.
As described above, the deposited film deposited on the inside of the chamber is removed by dry-cleaning by using the etching gas such as ClF3. By the way, after the cleaning by using the etching gas such as ClF3, it is necessary to sufficiently purge the residual etching gas (displacement purge) in the chamber, before ordinary CVD processes after the cleaning are performed.
However, since the etching gas such as ClF3 contains halogen of high electronegativity, then the etching gas adsorbed in the chamber surface can not be sufficiently desorbed through a short-time purge treatment. As the result, conventionally, a long-time purge treatment has been required.
In a CVD mode in which it is sufficient that the chamber cleaning is performed in a low cleaning frequency, even long purge time after cleaning does not arise a serious problem. However, in a CVD mode in which cleaning needs to be performed every time a CVD process is performed, long purge time leads to a reduction in the throughput.